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pdfsvgmatplotlibinkscape

White gradient artifacts left over after converting an SVG file to PDF

I have an SVG file of a bar plot that I need to convert to a PDF. The bar plot was made in matplotlib, saved as a PDF and imported into Inkscape. I used Inkscape to add annotations to the figure and then export it back to a PDF to be used in a final document.

This is what the PDF file looks like going into Inkscape

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After adding text elsewhere on the figure and saving as a PDF I get the same plot with these white lines:

enter image description here

These are not your typical PDF render artifacts, rather a closer inspection shows that they have a gradient to them.

enter image description here

I think this is somehow a product of the SVG file. I have used an online SVG-to-PDF converter and the lines are still present. Additionally, I use this method to make all my figure, Matplotlib to Inkscape to PDF and I have not had this issue with any other figures.

Solution

  • I've found that Inkscape does this when you import a bar graph which has a shading type that is not the same as any of the preset Inkscape patterns. I've seen this exact issue when I've imported graphs from R programing language and excel so I don't think it's specific to Matplotlib. I don't know the root cause, however, since I experience this problem a lot I'll share the workaround options I typically employ when I get this issue. One is not necessarily better than another and it depends on the situation which I use.

    Option 1) Convert the PDF to a .png bitmap image in some other program, (Gimp, Photoshop, Powerpoint....) then embed the image in Inkscape. Make your changes then export from Inkscape as a PDF. This has the disadvantage that the graph will no longer be a vector map. Use option 2 or 3 to keep it a vector map.

    Option 2) Import the pdf into Inkscape, ungroup the pdf object, delete the stripped filling in the bar graph, then recreate the filling using an Inkscape made fill. In the worst cases I've actually made custom bar graph patterns in Inkscape to exactly match the pattern that I had before. This process is a pain.

    Option 3) Create shapes that cover over the artifacts, remove border lines from the shapes and use the eye dropper to make them exactly the same color as the good parts.

    Like I said these are not an academic understanding of the problem to avoid the problem but I hope it can help you accomplish your task.